The present invention relates to an apparatus for continuously heating and drying stone aggregate useful in the production of asphalt paving composition or the like, and which also has the ability to incinerate contaminated soil under environmentally acceptable conditions.
The effective cleanup and disposal of soils which are contaminated with petroleum products and other contaminants have recently become major environmental concerns. As one specific example of the problem, a large number of underground fuel tanks have been found to be leaking and releasing a variety of contaminants into the surrounding soil, and as these tanks are being removed and repaired pursuant to environmental regulations, the volume of contaminated soil has been growing. Many communities no longer permit such soil to be placed in landfills, and thus a need exits for the decontamination of the soils.
Copending and commonly owned application Ser. No. 07/565,945 filed Aug. 10, 1990, discloses an apparatus for efficiently decontaminating soil, and wherein the soil is heated in the same rotary drum mixer used in the production of the asphalt. Thus the apparatus has several common components with a conventional asphalt production plant. This feature permits a conventional asphalt plant to be retrofitted by the addition of a relatively small number of additional components, so as to permit the apparatus to selectively produce asphalt, or to decontaminate soil.
Another known design for a soil decontamination apparatus which is utilized in combination with several of the components of a conventional asphalt plant, is disclosed in pending and commonly owned application Ser. No. 07/668,305, filed Mar. 13, 1991, and which comprises a drum dryer for heating aggregate in the conventional manner, and which includes a discharge end which is enclosed by a breaching for conveying the heated material to an external conveyor. A rotary soil incinerator is mounted adjacent the discharge end of the drum dryer, and the incinerator includes a discharge end which communicates with the breaching so that the incinerated soil may be discharged into the breaching and mixed with the heated aggregate. While the apparatus described in this latter application is very satisfactory, each unit must be customed designed and built, and the rotary soil incinerator cannot be standardized and used to retrofit existing dryers in view of the large number of different designs of such dryers.
Still another known soil decontamination apparatus involves a conventional aggregate dryer which is fitted with a slowly rotating combustion chamber adjacent the burner. The soil is fed into the rotating combustion chamber where it is incinerated, and the incinerated soil is then mixed with the aggregate. This apparatus is also generally satisfactory in operation, but is involves a high initial capital cost, and the operating cost is significant since the rotating combustion chamber is subject to deterioration even when soil is not being processed. Also, the incinerated soil is necessarily added to the heated aggregate whenever aggregate is being processed, and there is no opportunity for the separate use of the soil.
It is accordingly an object of the present invention to provide an aggregate dryer and soil incinerator wherein the soil incinerator is separate from the dryer and may be of standard construction so as to be adapted for use in association with dryers of different constructions.
It is another object of the present invention to provide an aggregate dryer and soil incinerator wherein the incinerator is of standard or universal design and may be used to retrofit existing dryers.
A further object of the present invention is to provide an aggregate dryer and soil incinerator wherein the incinerated soil exiting the incinerator can be selectively diverted so as to be mixed with the aggregate heated in the dryer, or separately utilized so as to not require that the soil be added to the aggregate.
It is still another object of the present invention to provide an aggregate dryer and soil incinerator wherein the volatile hydrocarbons contained in the gaseous products of combustion in the soil incinerator are further incinerated in the dryer to prevent a harmful discharge to the atmosphere.